This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No. 2000-403155 filed in Japan on Dec. 28, 2000, the entirety of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to an engine valve timing transmission apparatus, and more particularly, to an apparatus where a timing chain is arranged around a drive sprocket and a driven sprocket respectively fixed to a crankshaft and a valve camshaft. An end of a tensioner, press-contacted with an outer side surface of the timing chain to apply tension to the chain is swingably attached to an engine main body via a pivot pin.
2. Description of the Background Art
A similar engine valve timing transmission apparatus is described in Japanese Published Unexamined Patent Application No. Hei 7-71543. In this type of engine valve timing transmission apparatus, a pivot pin of a tensioner is held between junction surfaces of a crankcase divided in two halves to rotatably hold a crankshaft.
However, the pivot pin is too close to a timing chain, and the tensioner cannot be provided in an optimum position for tensioning of the timing chain. Further, since the pivot pin must be attached between the junction surfaces of the crankcase when the crankshaft is held between the two halves of the divided crankcase, assembly is difficult and unreliable.
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
An object of the present invention is to provide an engine valve timing transmission apparatus which increases freedom of attachment positions of the pivot pin.
A further object of the present invention is to enable placement of the chain tensioner in an optimum position for easy, reliable tensioning of the timing chain.
A further object of the present invention is to enable attachment of the pivot pin after assembly of the crankcase in order to improve the ease of assembly.
These and other objects are accomplished by an engine valve timing transmission apparatus comprising a timing chain engaging with a drive sprocket and a driven sprocket respectively fixed to a crankshaft and a valve camshaft; a chain tensioner, the chain tensioner having a first end press-contacted with an outer side surface of the timing chain to apply tension to the timing chain and swingably attached to an engine main body via a pivot pin; a timing chamber formed in a side wall of the engine main body for accommodating the timing chain; an opening having a diameter greater than the drive sprocket is provided on a side of the drive sprocket on an outer side wall of the timing chamber; and a lid plate for covering the opening is removably secured to the engine main body.
The pivot pin is held between opposite walls of the engine main body and the lid plate. The pivot pin can be reliably supported by the engine main body and the lid plate without special dropping preventing means. Further, the freedom of attachment position of the pivot pin in opposite walls of the engine main body and the lid plate increases, the pivot pin can be provided in a desired position, and the chain tensioner can be provided in an optimum position for tension of the timing chain. Furthermore, since the attachment of the pivot pin is made upon attachment of the lid plate, e.g. after assembly of the engine main body, ease of reliable assembly is improved.
Further, according to a second feature of the present invention, the engine main body is constructed with a cylinder block, a first crankcase half body connected to one end of the cylinder block, and a second crankcase half body connected to and in cooperation with the first crankcase half body and rotatably holding the crankshaft. The timing chamber is formed from the cylinder block to the second crankcase half body. The opening is provided over the first and second crankcase half bodies, and the pivot pin is held between opposite walls of the lid plate to close the opening and the second crankcase half body.
The pivot pin can be provided sufficiently away from the drive sprocket to the opposite side of the driven sprocket. Accordingly, a sufficient length of the chain tensioner can be ensured. The timing chain can be held under an approximately constant tension without influence by the extension of the chain, and the durability of the timing chain can be improved.
Further, according to a third feature of the present invention, a stator of a generator driven by the crankshaft is fixed to the lid plate. The lid plate also serves as a support base of the stator of the generator. This third feature permits a reduction in the number of parts.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.